It has long been known in the art to drive a conveyor chain, such as utilized on armored face conveyors, by means of a specially designed sprocket including spaced teeth for engaging the sequential horizontal links of the chain. While such a drive system is efficient and effective for this and other purposes, rapid wear of the teeth can be a serious problem. Specifically, the harsh operating environment of mining equipment is the primary cause of tooth wear. As a result of heavy loading, relatively high operating speeds and the presence of particulate material, including coal fines, sand, and small rock particles, trapped at the driving interface between the sprocket tooth and chain, wear is accelerated. Accordingly, the service life of the sprocket is drastically reduced.
As a result, productivity is lost through the need to relatively frequently take the conveyor out-of-service for repair. To a lesser degree, conveyor drive chains are vulnerable to this wear and must be periodically repaired or replaced. More specifically, as the driving face of the sprocket teeth wear, the conveyor flights, each including a crossbar and clamp, that pass through selected, spaced horizontal links for pushing the coal or other aggregate material, eventually come into contact with the teeth. This results in interference and jamming of the conveyor. The interference engagement occurs between the trailing face of each flight and the leading flank of the next tooth. When this occurs, it usually necessitates replacement of the entire sprocket, which is not only time consuming, but very costly.
In the prior art, sprockets have typically incorporated teeth with a symmetrical profile, that is the point of each tooth is centered with respect to its root and body. In this way, substantially equal clearance is provided between the flights at the point where they extend through the horizontal chain links, and both flanks of the teeth. This approach does allow for maximum clearance between the flights and the teeth in both directions for efficient bidirectional operation of the conveyor.
However, the one drawback of this design is that most of the wear on the teeth of a sprocket in mining conveyors, and in other similar applications, occurs in the predominately utilized, forward driving direction. Hence, sprocket teeth of symmetrical design adapted for bidirectional operation inherently compromise the overall service life of the sprocket. There is no compensation for the uneven wear that typically occurs. It has been discovered that surprisingly once a typical bidirectional tooth is worn to a point of interference with the flight, there is still plenty of strength left in the tooth to operate for an extended time. But for the interference that occurs, the conveyor could continue to operate for many more productive hours before being taken out-of-service for repair.
One prior art method for addressing this general wear problem is disclosed in U.S. Pat. No. 4,095,478 to Rynik. The Rynik patent discloses a drive sprocket for mining machines wherein every other tooth is removed. The theory is that part of the load on the teeth is relieved by the frictional engagement of the chain with the sprocket hub, and therefore wear of the remaining teeth is reduced. In practice, however, this approach has proved unsatisfactory. The frictional engagement force is simply not sufficient to compensate for the direct driving engagement force lost by removal of the teeth. Particularly in modern conveyors with driving requirements of several hundred horsepower, this prior art arrangement does not work well, and thus the concept remains unadopted in the industry. No other known prior art arrangement identifies, much less provides a feasible solution to the problem.
A need is therefore identified for a new approach in addressing the wear problem of sprockets, and particularly for providing a longer service life for sprockets particularly adapted to be utilized on heavy equipment in harsh environments, such as on mining conveyors.